Cathodic protection of printing apparatus

ABSTRACT

A rotary printing machine for fabrics which includes a color box containing a printing paste constituting a liquid electrolyte, a rotatable print roll having an engraved cylindrical outer printing surface, a rotatable brush roll in the color box for supplying to the printing surface an excess of printing paste as the print roll rotates, a steel doctor blade with a horizontally extending longitudinal edge positioned against the printing surface to remove the excess printing paste for gravity flow across one side of the blade in a direction perpendicular to its edge and a printing cylinder traversing and pressing a fabric web against the print roll printing surface following supplying of the printing paste thereto by the brush roll and after removal of the excess by the doctor blade. The doctor blade has a more electropositive strip of metal, such as magnesium, or aluminum, in electrical contact with the steel doctor blade spaced from the edge thereof and extending generally throughout the length thereof on said one side for flow of the excess printing paste thereacross in electrical contact therewith, thereby providing a sacrificial anode to prevent electrolytic corrosion and pitting of the doctor blade edge.

llnited States Patent [72] Inventor Erling B. Owren Foster,R.1. [21]AppLNo. 864,731 [22] Filed Oct. 8,1969 [45] Patented Nov. 30, 1971 [73]Assignee Cranston Print Works Company Webster, Mass.

[54] CATIIODIC PROTECTION OF PRINTING APPARATUS 6 Claims, 3 DrawingFigs.

[52] U.S.Cl 204/148, 101/l57,101/169 [51] 1nt.Cl B41f9/10, C23fl3/00[50] FieldofSearch 101/148, 157,169;204/147,|48,196,197

[5 6] References Cited UNITED STATES PATENTS 1,777,914 10/1930 Davis204/197 1,895,125 l/1933 Durham.. 101/148 2,283,169 5/1942 Atwood204/197 2,404,689 7/1946 Carlsenetal. 101/169 2,752,308 6/1956 Andrus204/106 Primary Examiner-T. Tung Anorney-Martin Kirkpatrick ABSTRACT: Arotary printing machine for fabrics which includes a color boxcontaining a printing paste constituting a liquid electrolyte, arotatable print roll having an engraved cylindrical outer printingsurface, a rotatable brush roll in the color box for supplying to theprinting surface an excess of printing paste as the print roll rotates,a steel doctor blade with a horizontally extending longitudinal edgepositioned against the printing surface to remove the excess printingpaste for gravity flow across one side of the blade in a directionperpendicular to its edge and a printing cylinder traversing andpressing a fabric web against the print roll printing surface followingsupplying of the printing paste thereto by the brush roll and afterremoval of the excess by the doctor blade. The doctor blade has a moreelectropositive strip of metal, such as magnesium, or aluminum, inelectrical contact with the steel doctor blade spaced from the edgethereof and extending generally throughout the length thereof on saidone side for flow of the excess printing paste thereacross in electricalcontact therewith, thereby providing a sacrificial anode to preventelectrolytic corrosion and pitting ofthe doctor blade edge.

CATI-IODIC PROTECTION OF PRINTING APPARATUS This invention relates torotary printing machines and more particularly to novel apparatus andmethods for preventing electrolytic corrosion and pitting of the edgesof doctor blades when used with printing rolls in such equipment.

As set forth in my earlier U.S. Pat. No. 3,l66,487, in known rotaryprinting machines for textile fabrics, and the like there is included areservoir called a color box, containing a printing paste constituting aliquid electrolyte, which is spread upon a rotatable print roll havingan engraved cylindrical outer printing surface by a rotatable brush rollin the color box. A steel or other metallic doctor blade with ahorizontally extending longitudinal edge is positioned against theprinting surface to remove excess printing paste from the unengravedportions of the print roll. A printing cylinder is also provided fortraversing and pressing a fabric web against the print roll printingsurface following supplying of said paste thereto by said brush roll andafter removal of the excess by said doctor blade, with enough pressurebetween the print roll and printing cylinder to transfer or print thepaste from the engraved depressions to the moving fabric. If the doctorblade does not remove all the unwanted excess printing paste from thesurface of the engraved print roll, streaks will be left on the rollwhich will appear as undesirable stripes on the fabric when the printingcylinder applies the fabric against the print roll. Any cracks, nicks orother unevenness in the edge of the doctor blade must therefore beavoided or unsalable streaked printed fabric will be produced. But,unfortunately, it has been long known that deleterious pitting andcorrosion of the edge of the doctor blade frequently appeared afteroperation of such roller printing equipment for a relatively shortperiod of time.

As a result of the development work leading to the inventions of my US.Pat. No. 3,166,487, it was discovered that such corrosion and pitting ofthe edge of the doctor blade is largely due to the electrolytic actionoccurring in a voltaic cell which includes the usual steel doctor bladeas the anode; the printing paste as the liquid electrolyte and the colorbox and print roll in contact with the paste as the cathode of the cell.The inventions of that patent approached the solution to the problem byadding an electrode to the color box and applying a small direct currentthereto which transferred the corrosive etching or pitting action to theinterposed electrode.

It is the major object of the present invention to solve the corrosiveetching and pitting problems of doctor blades in rotary printingmachines in a much simplified yet even more effective manner, and at thesame time eliminate the inconvenience of having to utilize supplementaldirect current for such control.

The above and further objects of the invention are accomplished bymounting on the doctor blade in electrical contact with it and with theprinting paste flowing across it a strip of metal more electropositivethan that of the doctor blade. Such strip is preferably spaced from thedoctor blade edge and extends generally throughout the length thereof.It may be of aluminum or magnesium to act as a sacrificial anode for thesteel doctor blade to prevent electrolytic corrosion and pitting of thedoctor blade edge.

Other objects and features of the invention will be apparent from thefollowing description of a preferred embodiment of the invention,together with the accompanying drawings, wherein:

FIG. 1 is a vertical section through the active printing parts of aroller printing machine showing somewhat diagrammatically one form ofthe present invention applied thereto;

FIG. 2 is an enlarged sectional view of the doctor blade portion of FIG.1, and

HO. 3 is an enlarged partial elevational view of the doctor bladeportion of FIG. 2. In the rotary printing machine shown in the drawings,there is included a color box 12 which contains the printing paste l4constituting a liquid electrolyte.

A rotatable fiber or nylon brush roll 16 clips into the reservoir ofprinting paste 14 in said color box and upon rotation carries the pasteand spreads onto the engraved cylindrical outer printing surface ofrotatable print roll 18 an excess of said paste as said print rollrotates. Print roll 18 has on its outer surface a repetitive design inthe form of depressions 19 for carrying the printing paste to be appliedto the fabric F. It is from the depressions 19 on this roll that thepaste is printing or applied against the fabric F, carried by thetraversing printing machine cylinder 22 past the print roll to transferor set" the engraved design on the fabric.

The printing paste 14 being supplied in substantial excess to thesurface of print roll 18, there is provided a doctor blade 24, generallyof steel, having a horizontally extending longitudinal edge 26positioned against the surface of the print roll 18 in advance of theplace where the roll reaches the fabric, so

.that the excess printing paste I4 is removed for gravity flow acrossone side of the doctor blade, and in a direction perpendicular to saidedge as shown by arrows 14a. The excess printing paste 14 is thusremoved from the print roll 18 and is returned to color box 12 bygravity flow. The doctor blade 24 is firmly but adjustably secured as bya mounting bar 28 on a suitable portion of the frame of the machine sothat the engagement of the edge of the blade with the surface of theprint roll may be carefully adjusted and maintained. A clamping bar 30,held in place as by a series of bolts 32 assists in securing the bladeto the mounting bar in proper position.

According to the present invention, there is provided, clamped betweenclamping bar 30 and mounting bar-28 and extending thereabove, a novelstrip 34 of a metal more electropositive than the metal of doctor blade24. As so clamped, strip 34 is in electrical contact with the doctorblade 24, spaced below the edge 26 thereof and extending generallythroughout the length of the doctor blade on the side thereof acrosswhich the excess printing paste flows, so that strip 34 is in electricalcontact with the excess printing paste flowing downwardly across it andmounting bar 28 for return to color box 12. Metals such as aluminum andmagnesium have been utilized as strip 34 and have been highly effectivein eliminating electrolytic corrosion and pitting ofthe doctor blade.

ln carrying out the invention, it has been found to be important thatthe strip 34 extend generally along the entire length of the doctorblade, which is commonly of the order of 40 to 60 inches infabric-printing machines, and that sufficient excess printing paste beapplied to print roll 18 so that doctor blade 24 and strip 34 is bathedtherein throughout their entire length. Of course, the doctor bladessurface must slop downwardly for gravity flow of printing paste 14thereacross the strip 34 must be positioned on the leading side thereofon which such flow occurs. Under these circumstances, the inventionprovides a galvanic cell which includes the doctor blade and the stripas the dissimilar metal electrodes and the excess of printing paste asthe liquid electrolyte and provides a sacrificial anode in the metalstrip to prevent electrolytic corrosion and pitting of the edge of thedoctor blade.

Although the metal strip shown and described herein is in the form of aseparate strip clamped beside the steel doctor blade, it may as welltake other forms, such as metal sprayed or plated onto the doctorblades, for example, and metals other than aluminum, moreelectropositive than the metal of the doctor blade may be used as well.

What is claimed is:

1. In a rotary printing machine for fabrics which includes a color boxcontaining a printing paste constituting a liquid electrolyte arotatably print roll having an engraved cylindrical outer printingsurface.

a rotatably brush roll in said color box for supplying to said printingsurface an excess of said paste as said print roll rotates a doctorblade with a horizontally extending longitudinal edge positioned againstsaid surface to remove said excess for gravity flow across one side ofsaid blade in a direction perpendicular to said edge and a printingcylinder traversing and pressing a fabric web against said print rollprinting surface following supplying of said paste thereto by said brushroll and after removal of said excess by said doctor blade thatimprovement which consists of a strip of metal more electropositive thansaid doctor blade in electrical contact with said blade spaced from theedge thereof and extending generally throughout the length thereof onsaid one side for flow of said excess printing paste thereacross inelectrical contact therewith, thereby providing a sacrificial anode toprevent electrolytic corrosion and pitting of said doctor blade edge. 2.In a rotary printing machine as claimed in claim 1, wherein said doctorblade is of steel. 3. In a rotary printing machine as claimed in claim2, wherein said strip of metal is of the class including aluminum andmagnesium. 4. The method of preventing electrolytic corrosion in arotary printing machine for fabrics which includes a color boxcontaining a printing paste constituting a liquid electrolyte arotatable print roll having an engraved cylindrical outer printingsurface a rotatable brush roll in said color box for supplying to saidprinting surface an excess of said paste as said print roll rotates adoctor blade with a horizontally extending longitudinal edge positionedagainst said surface to remove said excess for gravity flow across oneside of said blade in a direction perpendicular to said edge and aprinting cylinder traversing and pressing a fabric web against saidprint roll printing surface following supplying of said paste thereto bysaid brush roll and after removal of said excess by said doctor bladecomprising providing a strip of metal more electropositive than saiddoctor blade in electrical contact with said blade spaced from the edgethereof and extending generally throughout the length thereof on saidone side for flow of said excess printing paste thereacross inelectrical contact therewith, thereby providing a sacrificial anode toprevent electrolytic corrosion and pitting of said doctor blade edge.

5. The method as claimed in claim 4, wherein said doctor blade is ofsteel.

6. The method as claimed in claim 5, wherein said strip of metal isaluminum or magnesium.

2. In a rotary printing machine as claimed in claim 1, wherein saiddoctor blade is of steel.
 3. In a rotary printing machine as claimed inclaim 2, wherein said strip of metal is of the class including aluminumand magnesium.
 4. The method of preventing electrolytic corrosion in arotary printing machine for fabrics which includes a color boxcontaining a printing paste constituting a liquid electrolyte arotatable print roll having an engraved cylindrical outer printingsurface a rotatable brush roll in said color box for supplying to saidprinting surface an excess of said paste as said print roll rotates adoctor blade with a horizontally extending longitudinal edge positionedagainst said surface to remove said excess for gravity flow across oneside of said blade in a direction perpendicular to said edge and aprinting cylinder traversing and pressing a fabric web against saidprint roll printing surface following supplying of said paste thereto bysaid brush roll and after removal of said excess by said doctor bladecomprising providing a strip of metal more electropositive than saiddoctor blade in electrical contact with said blade spaced from the edgethereof and extending generally throughout the length thereof on saidone side for flow of said excess printing paste thereacross inelectrical contact therewith, thereby providing a sacrificial anode toprevent electrolytic corrosion and pitting of said doctor blade edge. 5.The method as claimed in claim 4, wherein said doctor blade is of steel.6. The method as claimed in claim 5, wherein said strip of metal isaluminum or magnesium.